Multiple arc fluorescent lamp



April 2, 1963 c. E. SWANSON MULTIPLE ARC FLUORESCENT LAMP 2 Sheets-Sheet 1 Filed Sept. 6, 1960 INVENTOR. 634m 5 SWAn/sm/ BY 9 f4 9 April 2, 1963 c. E. SWANSON MULTIPLE ARC FLUORESCENT LAMP 2 Sheets-Sheet 2 Filed Sept. 6. 1960 BALLAST INVENTOR. 654M 5 Sum/$0M BY $51,1 ArfMA/f/Y BALLAST This invention relates to electric discharge lamps and more particularly to electric lamps of the fluorescent type having a plurality of arc-streams.

Many types of low pressure discharge lamps are currently in use today. One common type is the fluorescent lamp, which is a low pressure, positive column type of lamp, whose envelope is generally tubular in shape. The inside of the envelope is coated with a phosphor which is excited to produce light in the visible frequency range by the resonance radiation of an atom of a particular type of material. In a typical fluorescent lamp, mercury is utilized to provide the atoms which emit the resonance radiation. Visible light is produced by first ionizing the mercury and forming a plasma containing mercury atoms. When an electron collides with a mercury atom in the plasma the atom is raised to the first excited state. In going back to the normal state the atom emits a quantum of energy having a wavelength which is proportional to the energy lost in going from the first excited state back to the normal state. In the case of mercury atoms, the emitted energy has a wavelength of 2537 Angstroms. The emitted energy reacts with the phosphor on the inside of the envelope to produce visible light. The phenomena occurring in this type of lamp are well known and other lamps have also been constructed using not only mercury but other materials, for example, sodium, which emit radiation of difierent wavelengths.

It is well known that the lumen output of a fluorescent lamp is proportional to lamp current loading. Accordingly, a lamp of a given length has a higher lumen output for a given current loading than a lamp of the same length which has a lower current loading. It is therefore desirable to construct fluorescent lamps so that they are able to withstand higher current loadings thereby making the lamps have a greater efliciency. When this is done, a greater 1'- men output is obtained with fewer lamps operating at the higher current loadings.

In accordance with the present invention, in order to increase the current loading of a fluorescent lamp so that it can operate at higher than normal current loadings thereby obtaining higher lumen outputs, a plurality of arcstreams are established within a single lamp envelope. This is accomplished by providing on the inside of the lamp envelope a pair of electrodes (filament-cathodes) for each arc-stream and a separator member which allows the establishment of the plurality of arc-streams without interaction therebetween.

The plurality of arc-streams achieves one or more of the following desired conditions within the lamp to increase lamp lumen output: l) more surface area of phosphor exposed to the arc-stream, since there are a plurality of arc-streams; (2) an arc-stream length longer than the length of the lamp, since there is a plurality of arcstreams; and (3) a cross-section for the lamp which generally squeezes the cross-section of the arc-stream into a non-circular, substantially oval, shape between the separator member and the envelope wall so that the effective electron temperature of the plasma is increased, and the loss due to imprisonment of resonance radiation is reduced because of the close proximity of the arc stream to an envelope or separator wall. Also, according to the invention, still longer arc-streams and the exposure of more phosphor surface area to the arc stream are obtained by making the separator member twisted in helical form,

States atom:

3,084,271 Patented Apr. 2, 1963 thereby causing the arc-streams to travel a helical path- It is therefore an object of this invention to provide a fluorescent lamp having increased efliciency.

Another object of this invention is to provide a lamp having a plurality of arc-streams.

Still a further object of this invention is to provide a' fluorescent lamp with an arc-stream separator member in side of the lamp envelope. 7

Still another object of this invention is to provide a fluorescent lamp having a spiral separator member therein so that a plurality of spiral arc-streams may be produced.

Yet another object of the invention is to provide a fluorescent lamp having a separator member therein to allow the use of two arc-streams within the lamp envelope and providing separate pairs of filament-cathodes for each of said arc-streams.

Other objects and advantages of the present invention will become more apparent upon reference to the followspecification and annexed drawings in which:

FIGURE 1 is a perspective view partially .broken away of a lamp made according to the invention;

FIGURE 2 is a cross-section of the lamp taken along lines 22 of FIGURE 1;

FIGURE 3 is a detailed view of the filament-cathode stem mount structure;

FIGURE 4 is a cross-section of another embodiment of lamp having another type of separator member;

FIGURE 5 is a cross-sectional view of a lamp having spinal arc-streams; and

FIGURE 6 is a diagram of an electric circuit [for use with the lamp.

Referring to FIGURE 1, a fluorescent lamp has an envelope termed by a tube 11 of substantially cylindrical shape wh1ch is made of a suitable transparent vitreous.

material such as glass or quartz. The inside of the tube 11 has a phosphor coating 13 which is placed thereon in the conventional manner. The tube 1 1 is shouldered down at the ends 14 to accommodate a base member 16, which is fastened to each end of the tube. Each of the bases 16 has at the end thereof a contact member 17 which holds the lamp in a suitable fixture (no-t shown) and makes electrical current source.

Sealed into each end of the tube 11 is a stem mount 20, which is preferably made of glass or some other suitable material. The stem 20 (see FIGURE 3) has a tabulation 22 therein which terminates in an aperture 24 which communicates with the interior of the tube 11. The tube 11 is first exhausted and then filled with a suitable starting gas and fill gas mixture and a small amount.

of mercury (not shown) through the tubulation 22. The tubulation 22 is then tipped-0E. To form the filamentcathode structure, a plurality of ceramic tubes-26 are cemented to the top of the glass stem 20. The lead-in.

for the arc-stream. The filaments 32 may be of the standard triple-coiled tungsten type which are normally used in very high output fluorescent lamps. 7

A heat shield disc 30 having holes therein is placed over the ceramic tubes 26 on each stem mount 20 behind the filaments 32. The heat shields 30 create the major lamp cooling zones at the respective ends of the lamp. The cooling zones limit the mercury pressure so that maximum contact with the external ballast and ultra-violet radiation output is obtained from the lamp.

In the lamp described only two arc-streams are to be utilized so only two filament-cathodes need be provided at each end of the tube 11. Each filament-cathode 32 acts with the filament-cathode opposite it at the other end of the tube 11, and the material within the tube 11, to establish an arc-discharge stream therebetween. In order to form two distinct arc-streams and to prevent interaction therebetween, ayseparator member 35, is placed in approximately the center of the tube 11. -In the lamp of-FIGURES l and 2, the separator member 35 is formed by two sheets 37 and 38 of a suitable material, such as glass, vicor, quartz or a ceramic, which are spread apart to make contact with the inner wall of tube 11. The material forming the sheets 37 and 38 of the separator men1- her need not be transparent and in a preferred embodiment of the invention. the sheets 37 and 38 are made opaque and are polished to have a reflecting surface for improved reflectance of light. It should be realized that the material forming the separator member 35 should not be highly conductive, as this will tend to short out the arc-streams. However, in a preferred embodiment of the invention the member 35 is made slightly conductive to insure better starting of the lamp.

The plates 37 and 38 are held together at each end by a clamp 42 which is preferably cemented or heat pressed to, the plates. The complete separator 35 is held in place in the approximate center of the tube 11 by two springs 40 at each end of the tube which press against the inner wall of the tube and against the separator member 35 thereby holding it in place. If desired, the plates 37 and 38 may be fused to the inside of the tube, cemented or held by someother suitable means. The separator member 35 has both of its sides coated with the phosphor 13 along its entire length. 'Ihe separator 35 runs substantially the entire length of the, tube 11 and extends between the respective filaments at .each end of. the tube 11 thereby forming two separate arc-chambers 43 and 44. In order toisolate the arc-streams in the two chambers 43 and 44 from each other an insulated disc 45 is placed at each end. of the separator 35. The disc 45 is preferably attached to a clamp 42, and is formed of twooverlapping halves having a slight fold in the middle thereof. Therefore, when the disc .45 is inserted into the tube 11 and fastened to the end of the separator 35 the disc tends to straighten out and press against the inner wall ,ofthe tube. When the stern mount 20 of FIGURE 3 is inserted into the end of the tube ll'the heat shield 30, which is already attached to the ceramic tubes 26, presses against the insulating discAS, as shown in FIGURE 1.

As can, be seen, each of the arc-stream and 44 has-a filament 32 at each endthereof and. an arcstream can therefore be established in each chamber. The arc-streams are fairly well insulated from each other since the separator member 35 is made of relatively 11011? conducting-material which extends across the entire diameter of the tube 11 and substantially along the tubes, entire length to a point at each end such that the filaments 32 are separated. Also, the insulated discs45 tendv to prevent the arcs from folding over. the ends of the separator, 35 v and interacting with each other at the ends of thet bea t vIn operation, an arc is struck between a pair of filaments, 32. at opposite ends ofthe lamp in each of the chambers 43 and 44. Since theseparator member, 35 makes each of the chambers 43 and 44 substantially noncircularin oross-section, the arc therein, shown by. the lines 47 in FIGURE 2,-is squeezedto conform more 'to the shape of the respective chamber.

The. arc-stream cross-sectiontends to become more oval since it does not fill the spaces between the ends of the plates 37 and 38 and the tube inner wall. As pointed out before, this increases'the output of the lamp by inchambers 43 creasing the efficiency of enegy transfer from the arcstream to the phosphor wall.

By providing two arcs in a single tube, the length of the arc-stream in the tube is effectively doubled. Also, the amount of phosphor surface area exposed to the arcstream is made greater than the phosphor surface area which would be exposed in a circular tube of standard, single arc-stream construction. For example, the periphery of a T17 tube (seventeen one-eighth inch units of outside diameter) is 6.66 inches. In the lamp shown in FIGURE 1, for a T17 tube-the periphery of each of the chambers 43 and is 5.45 inches making a totalof 10.9

inches. A four foot T17 lamp made according to standard construction has only 320 square inches of phosphor surface area exposed to the arc-stream while a four foot T17 lamp made according to the present invention has 524 square inches of phosphor surface area exposed. This, as

7 pointed out previously, gives higher light output.

The use of the heat-shield 3th behind the filament-cathode 32 at each end of the lamp provides a cooling zone between the heat-shield and the end of the lamp. The cooling zone at each'end of the lamp limits lamp mercury pressure so that the greater temperatures due to higher current loadings do not efiect the lumen output. In a preferred embodiment of the invention, a fill-gas mixture of about 80 percent argon and 20% helium is also used to increase the plasma ion mobility. Both of these features aid in maintaining a high effective electron temperature which is necessary for peak efficiency of energy transfer from the arc-stream to the phosphor wall.

In order to obtain a higher efiiciency lamp, the separator member 35 may be curvedor twisted thereby forming a plurality of curved. arcs. In a preferred embodiment of the invention the separator is formed into a helicoid. The result of the use of a helical separator provides a longer arc-stream in each chamber. For example, using a helicoid which has a pitch of approximately 5 inches and in which the centerof the arc-stream is displaced approximately one inch from its highest to lowest position on each side of the separator member, the arcstream in a T17 lamp 8 feet long is increased by approximately one foot. Considering that with the present invention two arcs are produced, each are being nine feet long, a total arc-stream length of 18 feet is obtained.

Referring now to FIGURE 4, a cross-section of a lamp using a helical separator member is shown. This lamp has a single plate 50, made of a suitable material such as glass, quartz, or vicor. The edges of the glass plate 50 have glass cloth or some other suitable material 52 attached thereto in order to provide more flexibility and better insulation when the spiral separator 50 is inserted inside of the tube 11. Both of the faces of the plate 50 and the tube inner wall are coated with the phosphor 13. The other components of the lamp are the same as those previously described. In a preferred embodiment of the invention, the ends of the separator member 50 are left flat so that they can extend between the two filaments at each end of the lamp, as shown in FIGURE 1. As in the case of the lamp of FIGURE -1, two separate chambers '54 and 55' are formed and an arc is established in each of them. In this case, the chambers are helical due to .the helical separator 50 and the arc-streams travel a helical path in the chambers.

The arc-stream 47 in a chamber is flattened out to a substantially oval shape between the separator 50 and the inner tube wall, as shown in FIGURE 4. The arc-streams 47 intertwine around each other, as shown in FIGURE 5, muchlike the strands of a rope. In FIGURE 5, the outlinesof the arc-streams 47 are shown by the solid lines within a cross-section of the tube 11. The spaces between the arc-stream lines and the tube 11 are caused by the arc-streams not filling the spaces in the tube near where the glass cloth 52 makes contact with the tube inner wall.

Since the lamp of FIGURES 4 and 5, with the helical separator member 50, has an ovalarc-stream cross-section, increased arc-stream length, and more phosphor surface area, all of the advantages of increased efficiency are obtained as described with respect to the lamp of FIG- URE 1. It should be realized that the effective amount of exposed phosphor surface area and the path length of the arc-stream of the spiral arc lamp is increased over the same factors in the lamp of FIGURE 1 by a factor proportional to the pitch of the separator member 50. Therefore, the spiral double-arc tends to be more effective.

'FIGURE 6 shows an electrical circuit diagram for operating the lamps of the present invention. A respective pair of filaments for the upper arc-chamber is connected across an input line 63 through a ballast 6% in the conventional manner. In a similar manner the filaments for the lower chamber are connected across input line 64 through a ballast 61. The ballasts 60 and 61 are prefera-bly of the type which are utilized for power-groove or very high output lamps which run at approximately 1500 milliamperes per ballast. This allows a lamp loading of approximately watts per foot of lamp length for each arc-stream. Due to the plural arc arrangement of the present invention, 1500 milliamperes of current is applied to each arc-stream thereby producing a lamp with a loading of 50 watts per foot of lamp. In the circuit of FIGURE 6, a special base 17 having four prongs is needed, one prong to make contact with a respective wire of lines 63 and 64. However, by placing one filament of each arc-stream in parallel, a standard, recessed double contact base, such as is used in very high output lamps (1500 milliamperes), can be utilized so that the lamp can fit into standard fixtures.

A preferred manner of manufacturing the lamps described herein is accomplished by placing the separator member or 50 inside a clear tube and then securing it by springs 40. The fluorescent phosphor coating is then applied 'by the conventional method of raising a column of phosphor coating by air pressure to fill the entire tube and then releasing the column, leaving the entire separator member and inner tube wall covered with a thin coating of phosphor. The coated tube is then dried with a gentle flow of clean air and baked in a lehr or roller oven to clean out all traces of solvent and lacquer which was part of the phosphor coating The discs are mounted and both ends of the tube are sealed with the stem mounts 20 by a suitable fusing or heat sealing process. After assembly .and sealing, the lamp is exhausted through the exhaust tubulation 22 in a conventional manner. During the exhaust process, both filaments 32 on each end of the lamp are electrically connected to a power supply so that the emission coating thereon can be heated to drive off all trace of solvent and lacquer and to break down the emission powder to its active state. A small amount of mercury is then introduced into the tube and the argon or a mixture of argon and helium is introduced for the fill-gas. The tubulation is then tipped-01f and the bases -16 are then fastened to the ends of the tube.

While the invention has been described with respect to a standard fluorescent lamp of the mercury type, it should be realized that its principles are not limited thereto. The principles of the invention may be used with other types of lamps, for example, those using sodium as a radiation emitting material. Other types and shapes of tubes may also be utilized so that, for example, the arc-stream separator can be used with a tube having a non-circular cross-section, thereby obtaining the advantages of both structures. It should also be realized that plates other than the fiat and helical shape disclosed may also be utilized and that other processes than those described can be used in making the lamp.

It is therefore seen that a novel fluorescent lamp has been described in which a plurality of arc-streams are achieved by use of a novel filament structure and an arc-stream separating member. This lamp attains all the advantages attendant to increasing the arc-stream length,

6 making the arc-stream cross-section area non-circular, and exposing more phosphor surface area to the arcstream. Further, since the tube is not modified, a standard circular tube may be utilized so that all of its advantages of economical manufacture, high resistance to implosion, etc., are obtained.

Although a particular structure has been described, it should be understood that the scope of the invention should not be considered to be limited by the particular embodiment of the invention shown by way of illustration, but rather by the appended claims.

What is claimed is:

1. In an electric discharge lamp of the fluorescent type, the combination comprising a'substantially tubular outer envelope, a separator member inside of said envelope to form a plurality of separate chambers, ta filamentcathode at each end of said envelope in each of said chambers to establish an electric discharge are in each of said chambers between the filament-cathodes at each end of the respective chambers and a phosphor coating which responds to said discharge are on the inner Wall of said envelope and on said separator member.

2. An electric discharge lamp of the fluorescent type as set forth in claim 1, wherein said separator member is substantially flat, thereby forming a plurality of straight arcs and the phosphor is coated on both sides of said member along the length thereof.

3. An electric discharge lamp of the fluorescent type as set forth in claim 1, wherein said separator member is curved along its length, thereby forming a plurality of arcs which curve along the length of the separator member and the phosphor is coated on both sides of said member along the length thereof.

4. An electric discharge lamp of the fluorescent type as set forth in claim 3, wherein said curved separator member has flexible material at its edges to engage the inner wall of said envelope.

5. An electric discharge lamp of the fluorescent type as set forth in claim 1, wherein said separator member is substantially helical along its length, thereby forming two helical arcs which are intertwined around each other.

6. In an electric discharge lamp of the fluorescent type, the combination comprising a substantially tubular outer envelope, a filament-cathode structure sealed at each end of said envelope, each of said structures having two pairs of support rods and a lead-in wire brought into said envelope through each support rod, a filament-cathode connected between a respective pair of support rods, a ceramic heat shield mounted on said rods between the filament-cathodes on each structure and a respective end of the envelope, an insulated member mounted on said support rods between said heat shield and said filamentcathodes on each of said structures, a separator member extending substantially the length of the envelope between said insulated member on each of said structures, said separator member engaging the inner wall of said envelope, thereby forming two separate chambers within said envelope with a filament-cathode in each of said chambers at each end thereof, which establish an arc stream discharge thcrebetween, and a phosphor coating the separator member and the inner wall of said envelope along their respective lengths.

7. An electric discharge lamp of the fluorescent type as set forth in claim 6, wherein said separator member is substantially flat, thereby forming two substantially straight arcs.

8. An electric discharge lamp of the fluorescent type as set forth in claim 6, wherein said separator member is substantially helical, thereby forming two helical arcs which inter-twine around each other.

9. An electric discharge lamp of the fluorescent type as set forth in claim 8, wherein said helical separator member has flexible material at its edges to engage the inner wall of said envelope.

, 110. In an electric discharge lamp of the fluorescent type the, combination comprising a substantially tubular outer envelope, a separator memberof a length less than said envelope; means-for mounting said separator member inside of said envelope and intermediate the ends thereof to form two separate arc chambers in the area separated by said member, a filament-cathode at each end of; said envelope and extending into each-of said are chambers; torestablish an arc discharge in eachvof the chambers between the filament-cathodes at each end of the envelope, and" a heat shield adjacent each end of said separator member and located between each said filament-cathode and the end of the envelope adjacent the same to provide a cooling zone in the space between the heat shield and the respective end of the envelope.

1 1. An electric discharge lamp of the fluorescent type as set forth in claim 10 wherein said separator member is substantially flat thereby forming a substantially straight arc discharge in each of said chambers.

-12. An electric discharge lamp of the fluorescent type as set forth in claim l0 wherein said separator member is curved thereby forming a curved arc discharge in each of said chambers, the effective length of each arc discharge being longer than the length of the envelope.

References Cited inthe file of this patent UNITED STATES PATENTS 1,974,888 Barclay Sept. 25, 1934' 2,076,286 Warren et al. Apr. 6, 1937 2,346,522 Gessel Apr. 11, 1944 

1. IN AN ELECTRIC DISCHARGE LAMP OF THE FLUORESCENT TYPE, THE COMBINATION COMPRISING A SUBSTANTIALLY TUBULAR OUTER ENVELOPE, A SEPARATOR MEMBER INSIDE OF SAID ENVELOPE TO FORM A PLURALITY OF SEPARATE CHAMBERS, A FILAMENTCATHODE AT EACH END OF SAID ENVELOPE IN EACH OF SAID CHAMBERS TO ESTABLISH AN ELECTRIC DISCHARGE ARC IN EACH OF SAID CHAMBERS BETWEEN THE FILAMENT-CATHODES AT EACH END OF THE RESPECTIVE CHAMBERS AND A PHOSPHOR COATING WHICH RESPONDS TO SAID DISCHARGE ARC ON THE INNER WALL OF SAID ENVELOPE AND ON SAID SEPARATOR MEMBER. 